fix most warnings with rp2040 -wconversion

hw/bsp/rp2040/family.c

@@ -53,7 +53,7 @@
 //
 // This doesn't work if others are trying to access flash at the same time,
 // e.g. XIP streamer, or the other core.
-bool __no_inline_not_in_flash_func(get_bootsel_button)() {
+bool __no_inline_not_in_flash_func(get_bootsel_button)(void) {
     const uint CS_PIN_INDEX = 1;
 
     // Must disable interrupts, as interrupt handlers may be in flash, and we
@@ -170,6 +170,8 @@ void board_init(void)
 
 void board_led_write(bool state)
 {
+  (void) state;
+
 #ifdef LED_PIN
   gpio_put(LED_PIN, state ? LED_STATE_ON : (1-LED_STATE_ON));
 #endif
@@ -192,6 +194,7 @@ int board_uart_read(uint8_t* buf, int len)
   }
   return len;
 #else
+  (void) buf; (void) len;
   return 0;
 #endif
 }
@@ -205,6 +208,7 @@ int board_uart_write(void const * buf, int len)
   }
   return len;
 #else
+  (void) buf; (void) len;
   return 0;
 #endif
 }